Abstract
High-temperature Raman spectra of natural sillimanite, andalusite and kyanite were measured in the temperature range of 296–1273 K at ambient pressure. No phase transition was observed over the temperature range in this study. Raman modes for the three samples vary with temperature linearly. The temperature and pressure dependence of the force constants for Si–O stretching vibrations in Al2SiO5 polymorphs were determined. The isobaric mode Gruneisen parameters of sillimanite, andalusite, and kyanite were determined from the temperature dependent of present high-temperature Raman spectra and previous results of thermal expansion coefficients. The intrinsic anharmonic mode parameters were estimated and nonzero, indicating the existence of intrinsic anharmonicity for sillimanite, andalusite and kyanite. Based on Kieffer model, the thermodynamic parameters, including isochoric heat capacity and entropy, were calculated.
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